Chapter 16: Gene Regulation Flashcards
Using the trp operon as an example, explain the concept of an operon and the function of the operator, repressor, and corepressor
The operon is a cluster of regulatory sequences of nucleotides (A, T, G, C) that direct the formation of proteins.
The operator binds a regulatory protein (repressor)
A repressor is a protein that stops transcription from occurring by binding to the operon, and thus the operon from being expressed.
A corepressor is a regulatory molecule that activates a repressor to turn off expression of the operon.
In trp operon, tryptophan is a corepressor to the trp repressor, so once enough tryptophan has been produced the expression of the operon is inhibited.
Explain adaptive advantage of bacterial genes grouped into an operon.
By utilizing gene regulation, bacteria are able to utilize available nutrients with maximum efficiency. E. Coli and lactose
Explain how repressible and inducible operons differ and how the differences reflect differences in the pathways they control.
In repressible operons, the corepressor activates the repressor protein to inhibit gene expression. The repressor protein is inactive at rest.
In inducible operons, the inducer inactivates the repressor protein to promote gene expression. The repressor protein is active at rest.
Describe how the lac operon functions and explain the role of the inducer, allolactose.
The lac operon is repressed by an active repressor. Allolactose, as an inducer, inactivates that repressor. Allolactose is made from lactose, thus in the presence of lactose gene expression is promoted as repressors are inactivated.
Differentiate between positive and negative control. Give examples of each from the lac operon.
Negative control is when the expression is inhibited by a repressor protein. An example is how in the lac operon a repressor binds to the sequence when an inducer activates the repressor protein.
Positive control mechanisms require the presence of an activator protein before RNA polymerase will bind efficientally. An example is the CAP in the lac operon.
Explain how cAMP and catabolism activator proteins are affected by glucose concentration.
When glucose in present in the cell, cAMP production is decreased. cAMP does not activate CAP, which means the lac operon is expressed at a much lower level.
Define differential gene expression. At what level are genes usually expressed?
Every cell has the same DNA, but expresses different sequences depending on cell type, location in body, environment, etc.
Most of the differences in gene expression occur because of transcriptional regulation.
Describe the role of the transcription initiation complex.
The transcription initiation complex is the binding of transcription factors already bound to the promotor to RNA polymerase, orienting it to begin transcription by serving as an intermediate in “bonding” it to the promotor.
Define epigenetic inheritance
Inheritance of traits not directly involving a change in nucleotide sequences. Example, silencing gene expression by methylation of nucleotides (specifically cystine).
Distinguish between heterochromatin and euchromatin.
Euchromatin is lightly packed (often under active transcription, as promotor is exposed) and heterochromatin is densely packed and the promotor is not exposed.
Define control elements and how they influence gene transcription.
Promotors, enhancers, etc.
Regions of the DNA that regulate the expression of certain genes by binding transcription factors that effect the rate of transcription.
Explain the role of promotors, enhancers, activators, and repressors in transcriptional control.
The promotor is the sequence that binds transcription factors that bind to RNA polymerase II to begin transcription.
Enhancer sequence will facilitate the positive or negative regulation of transcription via the binding of regulatory proteins, AND CREATING A DNA loop in the transcription initiation complex.
Activators are regulatory proteins that facilitate gene expression when activated.
Repressors regulatory proteins that inhibit gene expression when activated.
Explain how gene expression can be regulated at the translational and post-translational level.
The rate of degeneration of eukaryotic mRNA can effect the expression of genes by affecting the rate of translation.
RNA interference (RNAi) is when single strand of non coding RNA sequences bind to mRNA and regulate translation. The two types are miRNA and siRNA.
miRNA binds to sequences in the 3 prime UTR of mRNA and inhibits translation in the event of imperfect pairing, and cleaves mRNA in the event of perfect pairing. It is produced in the genome.
siRNA is similar. It binds to complementary sequences of RNA, but always cleaves the RNA it binds to. It is produced from double-stranded RNA that is not produced by cells genome.
Translational regulation affects the rate at which translation occurs.
Post translational regulation involves a complex mechanism that changes the structure of produced proteins to change behavior. Degradation of proteins is also a form of post translational regulation.
